The invention is in the field of air motors, and in particular pertains to an air motor which is designed to reduce the drawbacks of air motors as currently perceived in industry, with the aim of replacing electric motors, especially in environments in which sealed, anti-explosion electric motors must be used, if electric motors can be used at all.
In many different industrial environments, such as chemical plants, refineries, gas companies and shipyards, motors must be used for ventilation, pumping and other purposes which must operate in a potentially explosive environment. A spark-ignited fire in such a facility could quickly and easily cause millions of dollars in damage with the ensuing possibility of the destruction of lives.
Consequently, explosion-proof electric motors are subject to very high quality control standards, and have special housings which contain the sparks that are an inherent part of the operation of any electric motor.
There are a number of drawbacks in using explosion-proof electric motors. However, these drawbacks are perceived in the industry as basically unavoidable, as they are inherent in the use of explosion proof motors.
First, every motor that is made explosion proof is necessarily considerably more expensive than a motor used in an environment in which the presence of relatively open sparks is not a problem. However, the expense does not stop at the motor itself. There is also additional expense in any switches used to control the motor, any connectors, and the wiring and junction boxes installed in the plant are also of special, and more expensive, construction. Naturally, quality control standards are higher. More parts must be inventoried to accommodate explosion proof and non-explosion proof installations, with the accompanying inventorying cost and the inherent possibility of accidentally switching the two with potentially disastrous results.
Liability insurance costs, both for motor manufacturers and users of spark-free electric motors, is an added burden on the cost. As with everything else involving liability, these costs are increasing at a disturbing rate.
Electric motors tend to be quite reliable, and require infrequent maintenance. Nothing runs forever, however, and when maintenance is required, explosion proof motors must be sent back to the factory to be repaired or rebuilt. Not only is this quite expensive compared to on-site repair, but in the event that the motor is essential and a backup is not available, entire operations can grind to a halt for the want of an operative explosion-proof motor.
An air motor would seem to be an obvious alternative to an electric motor, and particularly to an explosion-proof electric motor since no sparks are produced anywhere along the compressed air pipes, junctions, hoses or at the motor itself. There are several reasons that traditionally air motors have not been widely used. First, high-speed turbine driven air motors are considered to be less reliable than electric motors and subject to more frequent maintenance. Although low speed air motors used, for example, in stirring vats of paint at 800 RPM are used, and high torque air motors are used for brief intermittent operations such as for starting diesel engines, it has been thought in industry that high speed, high duty cycle air motors, which have rotors operating at 5,000 to 10,000 RPM 24 hours a day for long periods of time at a stretch, will frequently break down and require maintenance.
There is also the problem of the noise of high speed rotor-driven air motors. The rotor itself can be somewhat noisy and requires a muffler. On top of the rotor, the gears traditionally used to reduce the output speed and increase the torque of high speed turbine motors, themselves produce a considerable whine.
There is also an at least partially justifiable fear of air motors due to the propensity of the rotor to fragment at high speed. Traditionally the rotor has been made of metal, with the buckets of the bucket-type turbine rotor being milled into the periphery of a metal disc. At the extremely high speeds at which the rotors operate, if centrifugal force eventually succeeds in pulling the rotor apart so that it fragments, several relatively large projectiles are immediately formed which not only tend to destroy the interior of the motor, but could fly out and cause injury to personnel or equipment. Rotor fragmentation damage can be reduced or avoided by using a heavy motor casing, but then of course materials cost rise, and portability drops.
Vane-type air motors, which comprise about 80% of all air motors in use, are not generally run over about 800 RPM and require lubrication. They cannot be used for more than two or three hours at high RPM, and the rotors require frequent replacement. Despite these limitations, if possible vane-type motors are sometimes used in spark-free environments, with the frequent replacement of the vane rotor being accepted as part of the necessary operating expense. However, due to the speed restrictions, they are used more in vacuum pump applications than for ventilation.
There is a need for a versatile, light-weight high-speed air motor which operates relatively quietly, and takes advantage of state-of-the-art materials to produce a motor capable of replacing high duty cycle electric motors in industrial applications, and particularly explosion proof electric motors.